Fabian Steinberg

Neural Correlates of Dual-Task Walking: Effects of Cognitive versus Motor Interference in Young Adults

Walking while concurrently performing cognitive and/or motor interference tasks is the norm rather than the exception during everyday life and there is evidence from behavioral studies that it negatively affects human locomotion. However, there is hardly any information available regarding the underlying neural correlates of single- and dual-task walking. We had 12 young adults (23.8 ± 2.8 years) walk while concurrently performing a cognitive interference (CI) or a motor interference (MI) task. Simultaneously, neural activation in frontal, central, and parietal brain areas was registered using a mobile EEG system. Results showed that the MI task but not the CI task affected walking performance in terms of significantly decreased gait velocity and stride length and significantly increased stride time and tempo-spatial variability. Average activity in alpha and beta frequencies was significantly modulated during both CI and MI walking conditions in frontal and central brain regions, indicating an increased cognitive load during dual-task walking. Our results suggest that impaired motor performance during dual-task walking is mirrored in neural activation patterns of the brain. This finding is in line with established cognitive theories arguing that dual-task situations overstrain cognitive capabilities resulting in motor performance decrements.

Influence of cognitive functions and behavioral context on grasping kinematics

We have documented before that human grasping movements executed in an everyday-like context differ from those in a typical laboratory context. The differences were reduced by factor analysis to five orthogonal factors; we took this as evidence that at least five distinct sensorimotor functions are context-dependent. To better understand how context exerts its influence on the sensorimotor system, we now evaluate the relationship between context-dependence and cognitive abilities. Forty subjects participated in a laboratory task (L) where grasping was explicitly instructed, externally triggered, repetitive, and served no higher ecologically valid purpose, or in an everyday-like task (E) where the movements were implicitly instructed, volitional, part of a behavioral sequence, and served a valid purpose. We registered a wide range of kinematic, force, and gaze parameters. Subjects also completed a battery of cognitive tests. We observed multiple task-related differences between grasping parameters, which could be reduced to five orthogonal factors by factor analysis with varimax rotation. Cognitive scores could also be reduced to five orthogonal factors. Five significant correlations between cognitive and grasping factors were observed and could be attributed to a linkage of cognitive abilities with E, with L, or with both tasks. Our data confirm that grasping movements are context-dependent and that this dependence can be traced back to five orthogonal factors. The observed correlations between cognitive and grasping factors are consistent with the view that behavioral context influences the distribution of processing between the ventral and the dorsal cortical stream.

Cerebellar, but not Motor or Parietal, High-Density Anodal Transcranial Direct Current Stimulation Facilitates Motor Adaptation.

OBJECTIVES Although motor adaptation is a highly relevant process for both everyday life as well as rehabilitation many details of this process are still unresolved. To evaluate the contribution of primary motor (M1), parietal and cerebellar areas to motor adaptation processes transcranial direct current stimulation (tDCS) has been applied. We hypothesized that anodal stimulation of the cerebellum and the M1 improves the learning process in mirror drawing, a task involving fine grained and spatially well-organized hand movements. METHODS High definition tDCS (HD-tDCS) allows a focal stimulation to modulate brain processes. In a single-session double-blind study, we compared the effects of different anodal stimulation procedures. The groups received stimulation either at the cerebellum (CER), at right parietal (PAR), or at left M1, and a SHAM group was included. Participants (n=83) had to complete several mirror drawing tasks before, during, and after stimulation. They were instructed to re-trace a line in the shape of a pentagonal star as fast and accurate as possible. Tracing time (seconds) and accuracy (deviation in mm) have been evaluated. RESULTS The results indicated that cerebellar HD-tDCS can facilitate motor adaptation in a single session. The stimulation at M1 showed only a tendency to increase motor adaptation and these effects were visible only during the first part of the stimulation. Stimulating the right parietal area, relevant for visuospatial processing did not lead to increased performance. CONCLUSIONS Our results suggest that motor adaptation relies to a great extent on cerebellar functions and HD-tDCS can speed up this process. (JINS, 2016, 22, 928-936).

Human performance in a realistic instrument-control task during short-term microgravity

Previous studies have documented the detrimental effects of microgravity on human sensorimotor skills. While that work dealt with simple, laboratory-type skills, we now evaluate the effects of microgravity on a complex, realistic instrument-control skill. Twelve participants controlled a simulated power plant during the short-term microgravity intervals of parabolic flight as well as during level flight. To this end they watched multiple displays, made strategic decisions and used multiple actuators to maximize their virtual earnings from the power plant. We quantified control efficiency as the participants’ net earnings (revenue minus expenses), motor performance as hand kinematics and dynamics, and stress as cortisol level, self-assessed mood and self-assessed workload. We found that compared to normal gravity, control efficiency substantially decreased in microgravity, hand velocity slowed down, and cortisol level and perceived physical strain increased, but other stress and motor scores didn’t change. Furthermore, control efficiency was not correlated with motor and stress scores. From this we conclude that realistic instrument control was degraded in short-term microgravity. This degradation can’t be explained by the motor and/or stress indicators under study, and microgravity affected motor performance differently in our complex, realistic skill than in the simple, laboratory-type skills of earlier studies.

Context dependence of manual grasping movements in near weightlessness.

BACKGROUND We have shown before that human subject grasping performance differs in an everyday-like context with that observed in a laboratory context. The purpose of the present study was to determine whether reported deficits in weightlessness are more pronounced when grasping is performed as part of everyday-like behavior rather than as an isolated laboratory-type response. METHODS The grasping performance of 12 participants (ages 29 +/- 5 yr) during periods of near weightlessness in parabolic flights was compared. Subjects performed a typical laboratory task (L) where grasping was repetitive, externally triggered, purposeless, and attention-attracting, and an everyday-like task (E) where the movements were part of a rich behavioral pattern, internally initiated, purposeful, and little attended. We registered typical kinematic, force, and gaze parameters, and calculated their within-subject means and variation coefficients. RESULTS A global parameter comparison showed that the effects of weightlessness on grasping movements were task-dependent: means were more affected in task E (RMS scores 1.29 +/- 0.07 in L compared with 1.74 +/- 0.15 in E) and variation coefficients in task L (RMS score 4.92 +/- 0.53 in L compared to 3.00 +/- 0.22 in E). DISCUSSION The results suggest that the effects of weightlessness observed under laboratory conditions can under- or overestimate the effects that emerge during everyday routines.

High-definition transcranial direct current stimulation to both primary motor cortices improves unimanual and bimanual dexterity

While most research on brain stimulation with transcranial direct current stimulation (tDCS) targets unimanual motor tasks, little is known about its effects on bimanual motor performance. This study aims to investigate the effects of tDCS on unimanual as well as bimanual motor dexterity. We examined the effects of bihemispheric anodal high-definition tDCS (HD-atDCS) on both primary motor cortices (M1) applied concurrent with unimanual and bimanual motor training. We then measured the effects with the Purdue Pegboard Test (PPT) and compared them to a sham stimulation. Between a pretest and posttest, 31 healthy, right-handed participants practiced the PPT on three consecutive days and received - simultaneous to motor practice - either HD-atDCS over the left and right M1 (STIM, n=16) or a sham stimulation (SHAM, n=15). Five to seven days after the posttest, a follow-up test was conducted. Two-way ANOVAs with repeated measures showed significantly increased performance for all PPT-scores (p<0.001) in both groups. The scores for the right hand, both hands, and overall showed significant TIME x GROUP interactions (p<.05) with more improved performance for the STIM group, while left hand performance was not significantly altered. These effects were most pronounced in the follow-up test. Thus, we can conclude that a bihemispheric HD-atDCS of both M1s improves performance of unimanual and bimanual dexterity. The strength of the effects, however, depends on which hand is used in the unimanual task and the type of bimanual task performed.

The context dependence of grasping movements: an evaluation of possible reasons

Laboratory experiments typically examine grasping movements as isolated motor acts executed for their own sake. In real life, however, grasping is often part of complex and meaningful movement sequences. We have shown before that grasping characteristics differ substantially between these two behavioral contexts and that these differences can be reduced to five orthogonal factors. Now we evaluate the role of focused attention, movement speed and/or embedding in other behavior as possible causes for the observed context differences. Subjects grasped in three variants, which deviated from our standard laboratory condition in one of the above three ways: In one, subjects’ attention was withdrawn from grasping by a concurrent visual memory task; in a second, subjects were pre-trained to grasp as slowly as in our standard everyday-like condition; and in the third variant, grasping was part of a more complex behavioral sequence. Grasping kinematics, grip forces and eye movements were registered across 20 repetitions of each variant, the outcome was normalized with respect to our standard laboratory and standard everyday-like conditions, and the normalized data were reduced to the underlying orthogonal factors. We found that the three variants of the laboratory condition had a non-uniform effect on grasping: decreasing the difference to the standard everyday-like condition for some factors, increasing it for others and leaving it unchanged for yet others. We interpret this finding as evidence that none of the three variants successfully reduced the difference between standard laboratory and standard everyday-like context; differences between contexts are therefore probably related to factors other than focusing of attention, movement speed and embedding in other behavior.

Effects of High-Definition Anodal Transcranial Direct Current Stimulation Applied Simultaneously to Both Primary Motor Cortices on Bimanual Sensorimotor Performance

Many daily activities, such as tying one’s shoe laces, opening a jar of jam or performing a free throw in basketball, require the skillful coordinated use of both hands. Even though the non-invasive method of transcranial direct current stimulation (tDCS) has been repeatedly shown to improve unimanual motor performance, little is known about its effects on bimanual motor performance. More knowledge about how tDCS may improve bimanual behavior would be relevant to motor recovery, e.g., in persons with bilateral impairment of hand function. We therefore examined the impact of high-definition anodal tDCS (HD-atDCS) on the performance of a bimanual sequential sensorimotor task. Thirty-two volunteers (age M = 24.25; SD = 2.75; 14 females) participated in this double-blind study and performed sport stacking in six experimental sessions. In sport stacking, 12 specially designed cups must be stacked (stacked up) and dismantled (stacked down) in predefined patterns as fast as possible. During a pretest, posttest and follow-up test, two sport stacking formations (3-6-3 stack and 1-10-1 stack) were performed. Between the pretest and posttest, all participants were trained in sport stacking with concurrent brain stimulation for three consecutive days. The experimental group (STIM-M1) received HD-atDCS over both primary motor cortices (M1), while the control group received a sham stimulation (SHAM). Three-way analysis of variance (ANOVA) revealed a significant main effect of TIME and a significant interaction of TIME × GROUP. No significant effects were found for GROUP, nor for the three-way interaction of TIME × GROUP × FORMATION. Further two-way ANOVAs showed a significant main effect of TIME and a non-significant main effect for GROUP in both sport stacking formations. A significant interaction between TIME × GROUP was found only for the 3-6-3 formation, indicating superior performance gains for the experimental group (STIM-M1). To account and control for baseline influences on the outcome measurements, ANCOVAs treating pretest scores as covariates revealed a significant effect of the stimulation. From this, we conclude that bilateral HD-atDCS over both M1 improves motor performance in a bimanual sequential sensorimotor task. These results may indicate a beneficial use of tDCS for learning and recovery of bimanual motor skills.

Title: fit2dive - A field test for assessing the specific capability of underwater fin swimming with SCUBA

Exercise modalities such as cycle ergometry do not mimic the specific movements of fin swimming underwater. Therefore, there is a need to develop a specific diving capability assessment procedure. The purpose of the study was the application of a standardized field test to assess and rate underwater swimming performance. The fit2dive-test consists of an incremental protocol that is performed in a pool (<5 m depth). The underwater swimming speed is increased stepwise by 0.2 m·s-1, starting with 0.4 m·s-1 until the subject’s subjective exhaustion is attained. Time of break-off (fit2dive-time), swimming technique (e.g. range of motion (ROM) of hip and knee joints) and equipment configuration was recorded via a standardized checklist. Subjects with the highest hip and knee flexion had lower fit2dive-times (373 ± 119 s; p<0.01) than those in the normal hip and knee flexion ROM category (448 ± 104 s). Further, divers using full foot fins had significantly higher (p<0.001) fit2dive-times (474 ± 97 s) than divers with adjustable strap fins (375 ± 104 s). The fit2dive test indicates the specific capability of underwater fin swimming. The results allow identifying weak factors such as underwater swimming technique or equipment configuration.

Brain Oscillatory and Hemodynamic Activity in a Bimanual Coordination Task Following Transcranial Alternating Current Stimulation (tACS): A Combined EEG-fNIRS Study

Motor control is associated with synchronized oscillatory activity at alpha (8–12 Hz) and beta (12–30 Hz) frequencies in a cerebello-thalamo-cortical network. Previous studies demonstrated that transcranial alternating current stimulation (tACS) is capable of entraining ongoing oscillatory activity while also modulating motor control. However, the modulatory effects of tACS on both motor control and its underlying electro- and neurophysiological mechanisms remain ambiguous. Thus, the purpose of this study was to contribute to gathering neurophysiological knowledge regarding tACS effects by investigating the after-effects of 10 Hz tACS and 20 Hz tACS at parietal brain areas on bimanual coordination and its concurrent oscillatory and hemodynamic activity. Twenty-four right-handed healthy volunteers (12 females) aged between 18 and 30 (M = 22.35 ± 3.62) participated in the study and performed a coordination task requiring bimanual movements. Concurrent to bimanual motor training, participants received either 10 Hz tACS, 20 Hz tACS or a sham stimulation over the parietal cortex (at P3/P4 electrode positions) for 20 min via small gel electrodes (3,14 cm2 Ag/AgCl, amperage = 1 mA). Before and three time-points after tACS (immediately, 30 min and 1 day), bimanual coordination performance was assessed. Oscillatory activities were measured by electroencephalography (EEG) and hemodynamic changes were examined using functional near-infrared spectroscopy (fNIRS). Improvements of bimanual coordination performance were not differently between groups, thus, no tACS-specific effect on bimanual coordination performance emerged. However, physiological measures during the task revealed significant increases in parietal alpha activity immediately following 10 Hz tACS and 20 Hz tACS which were accompanied by significant decreases of Hboxy concentration in the right hemispheric motor cortex compared to the sham group. Based on the physiological responses, we conclude that tACS applied at parietal brain areas provoked electrophysiological and hemodynamic changes at brain regions of the motor network which are relevant for bimanual motor behavior. The existence of neurophysiological alterations immediately following tACS, especially in the absence of behavioral effects, are elementary for a profound understanding of the mechanisms underlying tACS. The lack of behavioral modifications strengthens the need for further research on tACS effects on neurophysiology and behavior using combined electrophysiological and neuroimaging methods.